1. Field of the Invention
The present invention relates to an axle tube structure for a motor. In particular, the present invention relates to an improved axle tube that allows easy, reliable assembly of all of the elements of a motor.
2. Description of the Related Art
A conventional miniature heat-dissipating fan, as illustrated in FIG. 8 of the drawings, includes a circuit board 90 on which an axle tube 91 is formed. A stator 92 includes a central hole 94 that is force-fitted around the axle tube 91. A bearing 93 is mounted in the axle tube 91. The axle tube 91 is made of plastic material and is integrally formed with a plastic casing. In order to accurately assemble the bearing 93, the inner periphery of the axle tube 93 is processed by lathing or drilling to form an axle hole with a precise dimension for allowing force-fitting with the bearing 93. However, such a manufacturing process is troublesome. In addition, the stator 92, after assembly, cannot be reliably retained in place. Further, since the bearing 93 would generate heat when the rotor turns, the axle tube 91 expands as a result of heat expansion. Thus, the bearing 93 and the stator 92 cannot obtain the required force-fitting engagement therebetween. As a result, the rotor cannot turn stably, and noise occurs accordingly. Further, the stator 92 and the axle tube 91 may even disengage from each other.
It is the primary object of the present invention to provide an axle tube structure for a motor, wherein a reliable assembly is obtained without the risk of disengagement after the stator is force-fitted around the axle tube.
It is the secondary object of the present invention to provide an axle tube structure for a motor, wherein the axle tube includes an axle hole for easy, reliable engagement with two bearings that are coaxially engaged with an inner periphery defining the axle hole of the axle tube. Thus, the motor turns more smoothly and the noise is reduced.
An axle tube structure for a motor in accordance with the present invention comprises a casing having an axle tube. An inner periphery of the axle tube includes plural grooves each having an open upper end. An annular groove is defined in a bottom of the inner periphery of the axle tube. An engaging member includes a ring engaged in the annular groove of the axle tube and plural legs extending from the ring. Each leg is engaged in an associated one of the grooves of the axle tube.